Structure-based design of a bispecific receptor mimic that inhibits T cell responses to a superantigen.

Key surface proteins of pathogens and their toxins bind to the host cell receptors in a manner that is quite different from the way the natural ligands bind to the same receptors and direct normal cellular responses. Here we describe a novel strategy for "non-antibody-based" pathogen countermeasure by targeting the very same "alternative mode of host receptor binding" that the pathogen proteins exploit to cause infection and disease. We have chosen the Staphylococcus enterotoxin B (SEB) superantigen as a model pathogen protein to illustrate the principle and application of our strategy.

DNA repeats in the human genome.

Repetitive DNA sequences, interspersed throughout the human genome, are capable of forming a wide variety of unusual DNA structures with simple and complex loopfolding patterns. The hairpin formed by the fragile X repeat, (CCG)n, and the bipartite triplex formed by the Friedreich's ataxia repeat, (GAA)n/(TTC)n, show simple loopfolding. On the other hand, the doubly folded hairpin formed by the human centromeric repeat, (AATGG)n, the hairpin G-quartet formed by (TTAGGG)n at the 3' telomere overhang, and the hairpin G-quartet, and hairpin C+.

The high-resolution structure of the triplex formed by the GAA/TTC triplet repeat associated with Friedreich's ataxia.

Expansions of the triplet repeat, GAA/TTC, inside the first intron of the frataxin gene causes Friedreich's ataxia (FRDA). It was of interest to us to examine whether the FRDA repeat forms an unusual DNA structure, since formation of such structure during replication may cause its expansion. Here, we show that the FRDA repeat forms a triplex in which the TTC strand folds on either side of the same GAA strand.

Cystosine-rich strands of the insulin minisatellite adopt hairpins with intercalated cytosine+.cytosine pairs.

Previously, we reported the high resolution NMR structure of the hairpin G-quartet structure formed by the G-rich strand of the insulin minisatellite of repeat sequence, (ACAG4TGTG4/TGTC4ACAC4) located upstream of the human insulin gene. Here, we report structural studies on the C-rich strand of this insulin minisatellite. First, we show by high resolution NMR that (C4TGTC4) forms a hairpin dimer with intercalated C+.

Structure-function correlations of the insulin-linked polymorphic region.

The insulin minisatellite of the insulin-linked polymorphic region (ILPR), a 14 base-pairs long tandem repeat of: 5'-ACAGGGGTGTGGGG-3' 3'-TGTCCCCACACCCC-5', is located 363 base-pairs upstream of the human insulin gene. A locus for insulin-dependent diabetes mellitus (IDDM) has been mapped to the ILPR. It has been shown that the ILPR is polymorphic in length and this length polymorphism is also related to the transcriptional activity of the insulin gene and the susceptibility to IDDM.